A novel co-hydrolysis process, which applies dilute acid pretreatment directly followed by enzymatic saccharification without detoxification and liquid-solid separation between these two steps was implemented to convert lignocellulosic biomass into monomeric sugars. A factorial experiment in a randomized block design was employed to optimize the co-hydrolysis process for several herbaceous crops (switchgrass, giant reed, and miscanthus) and corn stover, with corn stover showing the greatest overall sugar conversion. Under optimal reaction conditions, corn stover exhibited a total sugar yield (glucose + xylose) of 0.545 g/g dry biomass at 83.3% of the theoretical yield. The oleaginous fungus Mortierella isabellina was selected and applied to the co-hydrolysate medium to accumulate fungal lipids due to its capability of utilizing both hexose (C6) and pentose (C5) sugars. Mass balance data from the M. isabellina fermentation served as the basis for developing a theoretical biorefinery utilizing fungal lipid for biodiesel production. The unit operations identified for the biorefinery are (1) corn stover collection and transportation, (2) pretreatment and enzymatic co-hydrolysis, (3) lignin processing, (4) fungal lipid fermentation, (5) fungal biomass drying, (6) lipid extraction and transesterification, (7) anaerobic digestion and aerobic treatment of wastewater, and (8) solar-bio-power generation. Energy life cycle analysis results show the assumed biorefinery system has a net energy output of -113.79 MJ/kg biodiesel produced. Overall, aerobic fungal lipid fermentation is shown to be the most energy-demanding unit operation, accounting for nearly 50% of all energy inputs, with co-hydrolysis resulting in large water and energy savings.
Read
